As shown in FIG. 1, the conventional plasma display device includes matrix-shaped plural anodes 20A and cathodes 40A respectively arranged between a front plate 10A and a rear plate 60A which are fixedly installed relative to each other by means of separating walls 30A. A black layer 50A is disposed between the cathode 40A and the rear plate 60A in order to improve contrast by absorbing external light. Such a plasma display device forms a certain pattern or picture by means of the plasma discharge light released from between the matrix-shaped cathodes and anodes. The brightnesses at the respective resolved picture elements (pixels) of the displayed picture are adjusted by the duration of the discharge and the intensity of the discharge.
The gray scale is determined either by supplying time-modulated pulses as illustrated in FIG. 24A, or by supplying amplitude-modulated pulses of FIG. 2B. However, in most cases, the gray scale is determined by a dual method through the variation of the current supplying time and the voltage level, that is, by supplying the amplitude/time-modulated pulses of FIG. 2C, thereby obtaining a gray scale through a wide range. But there is a limitation in increasing the gray scale through such a method, due to the fact that there are structural limitations such as invariable discharge region, the limitation of the physical characteristics of the cathodes, and the like.